Metal Matrix Composites (MMC) combine the properties of a metal matrix with reinforcing particulates thereby enhancing the mechanical properties of the end product. For example, an aluminum based MMC product will typically exhibit an increase in elastic modulus, lower coefficient of thermal expansion, greater resistance to wear, improvement in rupture stress, and in some instances, an increase in resistance to thermal fatigue.
Existing methods of fabricating MMC include squeeze casting, squeeze infiltration, spray deposition, slurry casting, and powder processing. The goal of these fabricating methods is to produce a uniform distribution of particulates throughout a metal matrix or to distribute the particulates near the outer surfaces of the metal product. For example, U.S. Pat. No. 4,330,027 describes a method of embedding particulate matter on the outer surface of a metal strip by forming a solidification front that pushes the particulate matter to the surface of the strip. In the past, however, fabrication of cast MMC into a finished product by rolling, forging, or extrusion has been impeded by the high loading characteristics of the particulate phase.
A need exists, therefore, for an aluminum based Metal Matrix Composite that combines the enhanced mechanical properties of MMC with improved ductility, appearance, and ease of fabrication. The present invention responds to this need by providing a functionally graded MMC with enhanced characteristics, comprising a central layer having a high density of particulates sandwiched between two outer metallic layers, and a method of manufacturing such a sheet.